1. Field of the Invention
The present invention relates to a burning damage protecting apparatus and method for a coil actuating a printing head in a printer.
2. Description of the Prior Art
In a conventional printer, a printing needle of the printing head is actuated by a solenoid. The solenoid includes a coil which is actuated by a driver. Printing operation in a printer is thus carried out by selectively actuating the driver. In such a driver actuating circuit for actuating a printing needle of the printing head, there was problem such that, when the driver is short-circuited, the coil is subjected to long-lasting continued electric current supply, thus resulting in a burning damage of the coil.
For this reason, there has been conventionally known a method detecting an abnormal condition as shown in the Japanese Unexamined Patent Application SHO 61-92876 in which a temperature detecting circuit detects an abnormal condition of the printing head before temperature of the heated coil generated in accordance with its operation reaches a dangerous temperature inducing a burning damage of the coil. Or, the Japanese Unexamined Patent Application SHO 59-5544 discloses a method in which a fuse provided in the driver actuating circuit opens the circuit when it is melted by temperature increase in the driver circuit.
Furthermore, regarding a method detecting a snapping of coil of the solenoid and non-conductivity of the driver in the driver actuating circuit, there has been known a method as disclosed in the Japanese Unexamined Patent Application SHO 59-109381, in which a connecting point between a coil and a driver of the solenoid is grounded through a large resistance, and there are provided a low-level detecting circuit for prioritizing a detection of low level signals and a high-level detecting circuit for prioritizing a detection of high level signals.
The detection of the snapping of coils is made on the basis of the output signal obtained when all the drivers are switched into an OFF-mode. On the contrary, the detection of the driver non-conductivity is made on the basis of the output signal obtained when all the drivers are switched into an ON-mode.
According to such conventional methods, it was possible to prevent coils actuating printing heads from burning by detecting abnormal conditions of the drivers and/or the coils during the printing operation of the printer. However, it was not possible to detect the abnormal condition of the driver before initiating the printing operation even if the printer is turned on.